John Nothard asks about a main bonding cable arrangement in an old house that has no earth cable installed. His question is answered by SELECT (Theme – Regulations & Legislation):
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This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: I'm in the process of upgrading the wiring system in a large old house that includes replacing three consumer units. My problem is that the main gas pipe and meter is a long way away at the other end of the building - and there is no earth cable installed.
The house has new carpets and has been redecorated, so the customer will not allow the floor boards to be lifted and there is no access through loft and no way to run the cable externally.
Is it acceptable to bond the pipework at the appliances and earth the mains gas pipe using a spike - making sure that it is a safe distance from the buried pipe?
Answer: Main protective bonding should not be confused with earthing! Main protective bonding is required to minimise touch voltages in the event of a fault while earthing is required where fault protection such as Automatic Disconnection of Supply is used to limit the duration of a fault i.e achieve disconnection within 0.4 secs or 5 secs.
Earthing the gas pipe via an earth electrode would therefore not meet the requirement for main protective bonding.
A main protective bonding conductor is normally installed from the main earth terminal to an extraneous-conductive-part and is usually a single-core insulated cable. However Regulation 543.2.1 permits other types of conductor, such as a metal covering of a cable (SWA) or an extraneous-conductive-part complying with Regulation 543.2.6 - e.g a metal water pipe, to be used for such purposes.
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